The Science Behind Olympic Curling

As the 2022 Winter Olympics rumble on in Beijing, here at PCS Instruments we thought we would focus on a very particular and interesting sport from the roster… Curling!

Curling is played by two teams who take it in turns to slide stones made of granite towards a target – known as the House, and whichever team has the most stones nearest the center of the house wins the points. But why is curling so interesting to us as an engineering company you might ask? Well as a company which focuses on friction and the development of machines which test frictional properties, curling applies to us more than almost any other.

This is because although curling teams and tactics are highly developed and skill focused (Olympic-level curlers can get the stones to within centimetres of where they were aiming), ironically, scientists still can’t agree on the fundamental physics of how curling works!

Were you to slide and spin any flat-bottomed object with a circular base along a flat surface, the object (say a glass on a table) would spin off in the opposite direction of the spin you placed on it; you spin the glass clockwise and it would move to the left, and vice versa.

This is due to the glass tipping forward as it moves, adding more weight to the leading edge, thus adding more friction to that leading edge. As the leading edge turns to the right, it’s met with more resistance than the back edge (which is turning to the left) does. Thus, the clockwise-spinning bottle follows the path of least resistance, curling to the left.

This applies to every object on earth except for one, and no extra points for guessing which one! Curling stones are the only object known to curl in the same direction as the spin put on them. Scientists have a variety of theories about why this happens, with two theories leading the way.

The first was proposed by Mark Shegelski from the University of Northern British Columbia, who theorised that the curling stone tips forward slightly as it slides (just like the glass). The added pressure warms the ice slightly and creates a thin film of water that can act as a lubricant. This in turn reduces the friction in the front to below the level at the back, essentially reversing the glass-on-table mechanism of friction.

The second leading theory is proposed by Harald Nyberg and his colleagues at Uppsala University. They propose that as the curling stone glides down the ice sheet, the contact surface (or running band) of the stone leaves scratches on the ice in the direction of rotation. The scratches are laid down by the leading edge of the running band, so that when the back edge glides over them it is very likely to follow them, causing the stone to curl in the direction of rotation.

Although both groups disagree with each other, they both agree that more research is needed on this unique physics phenomenon, and we at PCS Instruments agree! Any further study of friction is a good thing in our books.